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Pau Perez
square pixel and 4:3
on May 28, 2008 at 2:29:08 pm

Hi everyone. I suppose most of you work with NTSC, but I think I would have the equivalent doubts with that format as I have with PAL.

This is the point: Isn't PAL supposed to look 4:3 in it's final square pixel look in computer?

I mean, when I capture, the video has a flattened 768x576 look because of the non square pixel I suppose, although it says it is 720x576. So, looking flat it is 4:3. Now, when I compress it for example with the Flash encoder, it gains the non flatenned square pixel look and becomes really 720x576. But 720x576 is not 4:3. So the only way of having 4:3 in the computer is having it flattened?

This drives me nuts.


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Daniel Low
Re: square pixel and 4:3
on May 29, 2008 at 9:27:26 am

I'm not sure what you mean by the term 'flattened' in this instance but:

720x576 is 4:3 non-square pixels
768x576 is 4:3 square pixels.

All video encoded for computer playback should be square pixel as computer uses square pixels. Therefore, you would take a 720x576 source and transcode to flash at 640x480, 384x288 or 192x144 etc (Ideally you want to have the dimensions equally divisible by 16)








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Pau Perez
Re: square pixel and 4:3
on May 29, 2008 at 9:56:16 am

Sorry, by flattened I meant that it looks fat. The point is, if I want to see the video in the computer at 4:3 (768x576) it looks fat. Instead to see it properly I have to see it at 720x576, which is not 4:3!

When capturing and watching what's captured in any media player, it shows it 4:3 and flat. Later if I compress it with flash compressor, I can only do it at a ressolution equivalent to 720x576. The result is the image looks proportionally good, but not 4:3. The same with After Effects, when I say that I want to show it with square pixel, the image is no longer 4:3.



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Daniel Low
Re: square pixel and 4:3
on May 29, 2008 at 2:10:25 pm

I'm having a problem following you here, but how does the video look if you transcode it to 640x480 - which is 4:3

Perhaps you could explain the exact workflow you've used that produces 720x576 using square pixels (if that is what you believe is happening)

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Pau Perez
Re: square pixel and 4:3
on May 30, 2008 at 8:15:02 am

Well, the point is I can't transcode it to 640x480 without distorting it. When I write 640, it automatically writes 512. To change that I have to uncheck the "keep proportions".

So, I capture the video with Premiere for example, but I tried also with the window movie maker to see what would happen... it happens the same.

I get a squeezed video that looks 768x576 when seeing it in the media player or quicktime for example. When I transform it to square pixel (converting it to a .flv file, or interpreting the footage in After Effects) I get a normal looking image, no longer squeezed, but that in fact is 720x576.

If you want I can e-mail you 3 seconds of a captured video for you to see if that's normal or not.

My e-mail is paubcn@gmail.com



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Daniel Low
Re: square pixel and 4:3
on May 30, 2008 at 10:29:12 am

What are you capturing? DV?

What hardware are you using? Firewire?

What settings are you using for capture?

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Pau Perez
Re: square pixel and 4:3
on May 30, 2008 at 12:57:19 pm

Yep, I'm capturing DV and I use Firewire. I use the standard 48hz DV for Pal available in Premiere (image size 720x576 (1,067); 25f/s; milions of colours...)



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Daniel Low
Re: square pixel and 4:3
on May 30, 2008 at 2:46:36 pm

Ok. Transcode to 640x480 (or another 4:3 frame aspect and uncheck "keep proportions"



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Pau Perez
Re: square pixel and 4:3
on May 30, 2008 at 2:54:18 pm

But as a result it squeezes the image... So I assume it is impossible to have square pixel PAL videos in 4:3 without squeezing or cutting.

Thanks for your time anyway



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Daniel Low
Re: square pixel and 4:3
on May 30, 2008 at 5:32:43 pm

As i said in my 1st reply, 4:3 PAL can be either:

720x576 NON-Square pixels
or
768x576 Square pixels

If capturing PAL at 720x576 (non-square) and transcoding to 640x480 square pixels results in a distorted image then you have something wrong with some setting somewhere.

Are you sure you're not capturing 16:9 footage?





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Pau Perez
Re: square pixel and 4:3
on Jun 2, 2008 at 3:22:31 pm

Yes, I'm sure I'm not capturing 16:9 footage. In the after effects forum someone is telling me that PAL in square pixel looks in fact 720x576, that is 5:4. This is what he tells me:

---

It's the same encoded aspect ratio, for native PAL devices the resolution is always 720x576.

Only in the cases where you want to see what those 720x576 encoded pixels will look like when displayed would you need to scale the image (yes scale it, stretch it) out to 768x576.

However, this is not the way I would recommend to work, instead I would recommend placing your non-square footage into a matching non-square comp and enabling pixel aspect ratio correction preview (it looks like a small screen with a double sided arrow running horizontally through it, it's along the bottom of the comp preview pane). That way you are maintaining the same correct 720x576 encoded frame throughout the workflow.

To reiterate: unless you know what you're doing, it's best to always maintain the 720x576 resolution of the footage.

Whether the image is being displayed on a square pixel or non-square pixel device will determine whether those 720x576 pixels will appear to be 5:4 (square pixel device) or 4:3 (PAL device). We do not use different aspect ratios whether working on a square or non-square device, we just have to account for the different ways in which the same pixels are treated.



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Daniel Low
Re: square pixel and 4:3
on May 29, 2008 at 9:28:51 am

p.s. you might want to look at this:

http://kb.adobe.com/selfservice/viewContent.do?externalId=322300&sliceId=2





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